Method of manufacturing screens for cathode-ray tubes



'United States Patent M 4 Int. Cl. C09k 1/00; G03c 5/00; B44d 1/02 U.S.Cl. 96-361 6 Claims ABSTRACT OF THE DISCLOSURE A method of depositingindexing strips for a color television display tube in which a metalbacking layer supported by an organic film over a phosphor screen iswetter with an interrupted liquid layer before a hardenablephotosensitive binder layer is applied which is exposed to hardenportions thereof supporting the indexing strips.

The invention relates to a method of manufacturing screens forcathode-ray tubes for reproducing color images comprising a luminescentlayer containing at least two substances provided in discrete surfaceswhich luminesce in different colors upon excitation by electrons. Moreparticularly the invention relates to a method of wetting and coatingsuch a luminescent layer with a solution of an organic substance whichforms a film after drying. Thereafter, a metal layer pervious toelectrons is applied to this film. A substance which provides an indexsignal upon electron excitation then is applied to given areas with theaid of a photosensitive binder.

In such a cathode-ray tube, the luminescent layer generally containsthree substances luminescing in different colors, green, red and blue.These substances are provided in form of strips between which areinterposed strips consisting of a non-luminescent substance which isimpervious to light. The substance providing an index signal uponelectron excitation is furnished in the form of strips which occupy agiven position with respect to the strips of the luminescent layer.

The index signal may be obtained in different ways. Thus, if thesubstance consists of secondary-emission material, electron excitationresults in an electron current which then is collected on a collectorelectrode. In another case, the substance has the property that uponelectron excitation it emits radiation, generally ultraviolet radiation,which is collected in a photocell. The signals obtained in this mannerare used for the co ordination of the instantaneous modulation of theelectron beam, and the spot on the screen struck by the electron beam.

It has been customary to apply to the metal layer an organic film inorder to protect that layer because of its extreme thinness. For thispurpose, a solution of an organic substance which forms a film afterdrying is applied to the layer. If this solution is applied while theorganic film is still present below the metal layer, difficulties mayarise, since the thin metal layer always contains small pores throughwhich the solution of the organic substance may penetrate and may thusattack the subjacent organic film, resulting in damage to the metallayer.

If the solution is applied while the organic film is no longer presentbelow the metal layer, this implies that the screen is first baked outafter the application of the metal layer. This involves an additionalprocess, since after the application of the organic film and the sub-3,484,240 Patented Dec. 16, 1969 stance supplying an index signal uponelectron excitation the baking-out process must be repeated.

It has been found that especially in case of rectangular windows, theexpansion and contraction of the window involved in baking out aregenerally not entirely reversible. The correlation between the patternused in applying the discrete surfaces then no longer exists. Thesubstance supplying an index signal upon electron excitation mustaccurately occupy a given position with re spect to the discretesurfaces of the differently luminescing substances, which can no longerbe exactly attained in this case.

It is a principal object of the invention to provide a method ofmanufacturing a luminescent screen comprising at least two phosphorswhich luminesce in different colors in response to electron excitation,and which is provided with a thin metal layer and indexing strips inwhich damage to the layer is avoided and repeated bakeout steps areunnecessary.

This and further objects of the invention will appear as thisspecification progresses.

According to the invention, the electron pervious metal layer belowwhich the organic film is provided is wetted without the formation of anuninterrupted liquid layer and a solution of the photosensitive binderis spread thereon. The solution then is dried and exposed at the givenareas to the influence of hardening radiation to harden the binder.After removal of the non-exposed binder the screen is baked out.

In this method, the substance supplying an index signal upon electronexcitation may be applied in various ways. The solution of thephotosensitive binder may contain this substance in the form of asuspension, This substance is then already present at the given areasafter the exposure to the hardening radiation and at the other areas thesubstance is removed together with the non-exposed binder.

According to another method, the substance is not suspended in thesolution of the photosensitive binder. Consequently, in this case onlythe layer of binder is exposed to the influence of hardening; radiation.At the irradiated areas, the binder becomes insoluble, but if at leastthe irradiation is not continued for an excessively long time, itremains slightly sticky. The substance may subsequently be applied inthe form of a suspension, during which process it adheres to theslightly sticky annealed parts so that it is not washed away during thesubsequent removal of the non-exposed binder; or, the substance may beapplied in the form of a suspension after the non-exposed binder hasbeen removed. During the final baking-out of the screen, the binder 'ofthe luminescent layer, the organic film and the binder of the substancesupplying an index signal upon electron excitation are removed.

In this method, during the application of the photo sensitive hinder theorganic film is still present below the electron pervious metal layerwhich always contains small pores. When this layer is wetted, the liquidpenetrates through the po es into the organic film and, also, throughthis film into the luminescent layer. Gas bubbles then ascend which dueto the fact that the metal layer is not covered with a noninterruptedliquid layer can escape through the pores in the metal layer so thatthey do not damage the metal layer. The organic film provides asufficient strength for the metal layer so that the solution of thephotosensitive binder does not adversely affect the metal layer duringthe applica ion and the following processes. For wetting a liquid isused which does not attack the organic film, preferably a liquid whichcan readily be mixed with the solvent of the photosensitive binder. Itis advantageous to carry out the wetting process by means of spraying oratomization, during which processes fine drops are formed.

For the photosensitive binder, an aqueous solution of polyvinylalcoholin which a bichromate, for example, ammonium bichromate, serving as asensitizer may be used. For wetting, water or a mixture of water andalcohol may be used, for example. A dried layer of the solution can behardened by exposing it to a radiation having a wave length lyingbetween 3600 A. and 5000 A., whereupon the binder is no longer solublein water and alcohol.

In one embodiment the luminescent layer, which is composed ofdifferently luminescing strips with the interposition of non-luminescentstrips, is wetted with water. On this layer, an organic film is formedusing a solution of one or more methacrylates in toluene. An aluminumlayer is deposited by evaporation thereon in vacuo. By means of anatomizer, the aluminum layer is wetted with water. After the water hasbeen allowed to penetrate through the pores of the aluminum layer, anaqueous solution is applied which consists of polyvinyl alcoholcontaining as a sensitizer, ammonium bichromate, and in the form of asuspension, a cerium-activated calcium-aluminum silicate. After drying,given areas are exposed to radiation having a wave-length lying between3600 A. and 5000 A.

in a manner such that these exposed parts occupy a given position withrespect to the strips of the luminescent layer. The non-exposed partsare then rinsed away with water, whereupon the screen is baked out,during which process the binder of the luminescent layer, the organicfilm and the polyvinyl alcohol are burned out. Thus, strips ofcerium-activated calcium-aluminum silicate are present on the aluminumlayer which supply long wave-length ultraviolet radiation uponexcitation by electrons.

While the invention has been described in connection with specificembodiments and applications thereof, other modifications will beapparent to those skilled in this art without departing from the spiritand scope of the invention as defined in the appended claims.

What is claimed is:

1. In the method of manufacturing a luminescent screen for a cathode-raytube for reproducing color images comprising the steps of applying togiven areas of a transparent substrate a luminescent layer consisting ofat least two substances luminescing in different colors upon excitationby electrons, wetting and coating said luminescent .4 layer with asolution of an organic substance, drying said organic substance,applying a metal layer pervious to electrons to said film, and formingover a portion at said metal layer a strip of a substance supplying anindexing signal upon excitation by electrons the steps of wetting themetal layer with an interrupted liquid layer so as to penetrate saidmetal layer and first organic film, applying a solution ofphotosensitive binder on said liquid layer, drying the solution andexposing the same at areas corresponding to the location of the indexingstrip to the influence of hardening radiation, removing the unexposedbinder, and baking out the screen.

2. A method as claimed in claim 1, in which the solution of thephotosensitive binder contains in the form of a suspension the substancesupplying an index signal upon excitation by electrons.

3. A method as claimed in claim 1, in which the substance supplying anindex signal upon excitation by electrons is applied in the form of asuspension after the dried solution of the photosensitive binder hasbeen exposed at the said given areas to hardening radiation beforeremoving the unexposed binder and baking out the screen.

4. A method as claimed in claim 1, in which the substance supplying anindex signal upon excitation by electrons is applied in the form of asuspension after the nonexposed binder has been removed and beforebaking out the screen.

5. A method as claimed in claim 1, in which the photosensitive binder isan aqueous solution of polyvinylalcohol containing ammonium bichromate.

6. A method as claimed in claim 2, in which the suspension iscerium-activated calcium-aluminum silicate.

References Cited UNITED STATES PATENTS 7/1956 Barnett 9636.1 X 7/1961Kaplan et al ll7-33.5 X

U.S. C1.X.R. ll733.5

